1. Field of the Invention
The present invention relates to a brake system comprising an electric brake force generator or generating means that brakes a wheel by a driving force of an electric motor.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2005-343366 discloses a brake system of the type referred to as a brake by wire (BBW) brake system, which converts a braking operation of a driver into an electrical signal used to operate an electric brake force generator or generating means, such as a motor cylinder, and operates a wheel cylinder by brake fluid pressure generated by the motor cylinder.
When a problem occurs that renders inoperable an electric motor of an electric brake force generating means (slave cylinder) of the BBW brake system, or a problem that causes a seizure of a ball screw mechanism for converting a driving force of an electric motor into advance and retreat movements of a piston, it is required to perform a failsafe or backup process for braking by using brake fluid pressure generated by a master cylinder instead of the brake fluid pressure generated by the slave cylinder.
In order to determine whether the slave cylinder is functioning normally, it may be determined whether the electric motor is rotating normally or whether the piston is moving normally forward when the driver applies a pushing force to a brake pedal. However, in the system where the problem determination is performed based on the pushing force applied to the pedal by the driver, it is impossible to determine the occurrence of a problem before the driver applies the pushing force to the brake pedal to operate the slave cylinder, leading to a possibility that the backup process cannot be quickly performed upon the occurrence of the problem.